I think that the information on the developmental charts can be used by pediatricians to ensure that a child isn't delayed (thus, if the child isn't combining two words by the two-year checkup, they might check him for possible delays...).
The Denver II scale gives a much better perspective. It has over 100 different milestones. They're divided into broad groups (language, gross motor, etc.). The test shows ages at which as few as 25% of children can do something, and goes up to 90%.
A nice thing about Denver II is that is has lots of skill groups. My kids were well before the 25% point on some things (e.g. name 4 colors) and were ND on others (e.g. walk well).
That said, some of the milestones do highlight just different gifted kids can be. "Copy circle" (25% at ~3y3m) springs to mind for my DD4. She was drawing circles plus a few letters spontaneously when she was a couple months past two.
I once met a 7 month old baby who was walking (25% at 11+ months). That was something to see!
It's a pretty fascinating document.
Denver II Val
